Open Data supplied by Natural Environment Research Council (NERC)

Neil Brown MK3 CTD

The Neil Brown MK3 conductivity-temperature-depth (CTD) profiler consists of an integral unit containing pressure, temperature and conductivity sensors with an optional dissolved oxygen sensor in a pressure-hardened casing. The most widely used variant in the 1980s and 1990s was the MK3B. An upgrade to this, the MK3C, was developed to meet the requirements of the WOCE project.

The MK3C includes a low hysteresis, titanium strain gauge pressure transducer. The transducer temperature is measured separately, allowing correction for the effects of temperature on pressure measurements. The MK3C conductivity cell features a free flow, internal field design that eliminates ducted pumping and is not affected by external metallic objects such as guard cages and external sensors.

Additional optional sensors include pH and a pressure-temperature fluorometer. The instrument is no longer in production, but is supported (repair and calibration) by General Oceanics.

Aquatracka fluorometer

The Chelsea Instruments Aquatracka is a logarithmic response fluorometer. It uses a pulsed (5.5 Hz) xenon light source discharging between 320 and 800 nm through a blue filter with a peak transmission of 420 nm and a bandwidth at half maximum of 100 nm. A red filter with sharp cut off, 10% transmission at 664 nm and 678 nm, is used to pass chlorophyll-a fluorescence to the sample photodiode.

The instrument may be deployed either in a through-flow tank, on a CTD frame or moored with a data logging package.

SeaTech Transmissometer

Introduction

The transmissometer is designed to accurately measure the the amount of light transmitted by a modulated Light Emitting Diode (LED) through a fixed-length in-situ water column to a synchronous detector.

Specifications

Water path length: 5 cm (for use in turbid waters) to 1 m (for use in clear ocean waters).

Notes

The instrument can be interfaced to Aanderaa RCM7 current meters. This is achieved by fitting the transmissometer in a slot cut into a customized RCM4-type vane.

A red LED (660 nm) is used for general applications looking at water column sediment load. However, green or blue LEDs can be fitted for specilised optics applications. The light source used is identified by the BODC parameter code.

RRS Charles Darwin 58 and 59 CTD Data Documentation

Introduction

CTD profile data are presented from the VIVALDI '91 cruises Charles Darwin 58 and 59, as reported by Pollard et al. (1991). The data collection and calibration procedures have been described by Griffiths et al. (1992).

Instrumentation and Methodology

Instrumentation Summary

The CTD profiles were taken with a Neil Brown Systems MkIIIb CTD mounted beneath a bottle rosette. The CTD was fitted with a pressure sensor, conductivity cell, platinum resistance thermometer, a dissolved oxygen sensor, a Chelsea Instruments fluorometer, a Sea Tech 100cm path transmissometer and an IOS 10kHz pinger.

Data Acquisition

Lowering rates for the CTD package were generally in the range 0.5-1.0ms-1 but could be up to 1.5ms-1. CTD data were logged at 16 frames per second. The CTD deck unit passes raw data to a dedicated Level A microcomputer where 1 second averages are assembled. During this process the Level A calculates the rate of change of temperature and a median sorting routine detects and removes pressure spikes. These data are sent to the Level B for archival. The data are then passed to a Level C workstation for conversion to Pstar format and calibration.

A total of 19 stations were occupied during CD58 (11v01 - 11v19) and 21 stations during CD59 (12v01 - 12v21) using the MkIIIb CTD. The first 2 stations of CD58 were equipment test stations not on the Vivaldi grid and the data have not been passed on to BODC. During CD59 a Neil Brown MkV CTD was also used at 3 of the stations (12v12 - not 12v11 as sometimes reported in the cruise report, 12v16 and 12v17), but these data were not forwarded to BODC and are not reported here.

Data Processing

The 1 second data passed to the Level C were converted to Pstar format and initially calibrated with coefficients from laboratory calibrations. The up cast data were extracted for merging with the bottle firing codes, on time, thus the CTD variables were reconciled with the bottle samples. Final calibrations were applied using the sample bottle data.

The data were worked up to WOCE standards by the data originators before being supplied to BODC. Although an oxygen sensor was fitted to the CTD, the data originators considered that these data were not to WOCE standards. Subsequently, the data are not reported here and are not stored by BODC.

BODC Data Processing

No further calibrations were applied to the data received by BODC. BODC were mainly concerned with the screening and banking of the data.

The data were converted into the BODC internal format (PXF) to allow the use of in-house software tools, notably the graphics editor. Potential attenuance was converted to attenuance as follows:

atten = exp (-atten)

atten = atten / (1.0 -ln (atten) x press / 215800)

atten = -ln (atten)

Spikes in the data were manually flagged 'suspect' by modification of the associated quality control flag. In this way none of the original data values were edited or deleted during quality control. These data from the VIVALDI '91 cruises required little flagging and just a few points were set suspect. Chlorophyll was all null in profile 12v13.

Once screened, the CTD data were loaded into a database under the Oracle relational database management system. The start time is the CTD deployment time, and the end time is the time the CTD was removed from the water. Actually these times are more precisely the start and end of data logging. Latitude and longitude are the mean positions between the start and end times calculated from the master navigation in the binary merged file.

World Ocean Circulation Experiment (WOCE)

The World Ocean Circulation Experiment (WOCE) was a major international experiment which made measurements and undertook modelling studies of the deep oceans in order to provide a much improved understanding of the role of ocean circulation in changing and ameliorating the Earth's climate.

WOCE had two major goals:

Goal 1. To develop models to predict climate and to collect the data necessary to test them.

Goal 2. To determine the representativeness of the Goal 1 observations and to deduce cost effective means of determining long-term changes in ocean circulation.

UK WOCE

The UK made a substantial contribution to the international World Ocean Circulation Experiment (WOCE) project by focusing on two important regions:

VIVALDI, a seven year programme of seasonally repeated surveys to study the upper ocean.

Long-term observations of ocean climate in the North West Approaches.

Satellite ocean surface topography, temperature and wind data were merged with in situ observations and models to create a complete description of ocean circulation, eddy motion and the way the ocean is driven by the atmosphere.

The surveys were forerunners to the international Global Ocean Observing System (GOOS). GOOS was later established to monitor annual to decadal changes in ocean circulation and heat storage which are vital in the prediction of climate change.

Please note: the supplied parameters may not have been sampled from all the bottle firings described in the table above. Cross-match the Sample Reference Number above against the SAMPRFNM value in the data file to identify the relevant metadata.

Fixed Station Information

Station Name

WOCE Atlantic Area 12 (AR12)

Category

Offshore area

Latitude

52° 0.00' N

Longitude

18° 0.00' W

Water depth below MSL

World Ocean Circulation Experiment (WOCE) Atlantic Area 12 (AR12)

WOCE was a major international experiment which made measurements and undertook modelling studies of the deep oceans in order to provide a much improved understanding of the role of ocean circulation in changing and ameliorating the Earth's climate. WOCE established numerous areas and repeat sections in the Atlantic Ocean as illustrated in the map below.

AR12 spans the boundary between the subtropical and subpolar gyres in the eastern basin; stations lie within a box bounded by 40.0°N, 35.0°W at the southwest corner and 65.0°N, 03.0°W at the northeast corner The area was occupied between April 1991 to September 1998. A table of all AR12 cruises is presented below:

Related series for this Fixed Station are presented in the table below. Further information can be found by following the appropriate links.

If you are interested in these series, please be aware we offer a multiple file download service. Should your credentials be insufficient for automatic download, the service also offers a referral to our Enquiries Officer who may be able to negotiate access.